A standard self-tightening drill chuck normally has a chuck body adapted to be mounted on a drill spindle for rotation about an axis and formed with substantially cylindrical front and a rear outer surfaces both centered on the axis and axially offset from each other and with an outwardly open groove between the front and rear surfaces. A tightening sleeve surrounding the body is formed with substantially cylindrical front and rear inner surfaces both centered on the axis and riding on the front and rear surfaces of the body and with an inwardly open groove between the front and rear inner surfaces and forming with the groove of the body an annular generally circular-section passage. The cylindrical surfaces keep the sleeve and chuck body centered on each other. The front part of this sleeve, which is typically made of several pieces, is formed with a rearwardly flared substantially frustoconical seat also centered on the axis. Rollers riding in the grooves support the sleeve on the body so as to permit relative rotation of the body and sleeve about the axis while preventing relative axial displacement. A jaw guide in the sleeve is formed with a plurality of axially forwardly open and angularly spaced slots in which respective jaws that also ride on the seat are axially and radially displaceable.
These objects are attained according to my earlier U.S. Pat. No. 4,880,246 in a self-tightening drill chuck of the abovedescribed general type but having a spring unit braced axially between the guide and the chuck body and urging the guide axially forward to press the jaws axially forward against the seat. Thus with the system of this earlier invention the sleeve forming the jaw seat as well as the inner and outer cylindrical guide surfaces can be formed in the same turning operation, that is by the same lathe in the same production step, so all these surfaces will be absolutely perfectly coaxial. The sleeve will ride perfectly on center on the chuck body, which is similarly turned in one operation so its outer cylindrical guide surfaces are also perfectly coaxial, and the jaws will ride on the perfectly coaxial frustoconical jaw seat. The jaw guide therefore serves basically to keep the jaws angularly offset in the desired position, and itself is kept tightly in place on the jaw seat by the spring unit.
In this arrangement the guide and sleeve are formed with radially confronting pockets in which is received a locking ball that rotationally couples the sleeve and guide. One of the pockets is formed as an axially elongated slot so that there is some possibility of limited axial movement between the sleeve and guide. These pockets are formed at the rear end of the chuck, that is its end remote from the tool where torque is applied to the chuck so that some twisting and deformation of the chuck is possible. As a result the guide can get wedged in the sleeve and become canted and offcenter relative to the chuck body. Hence the self-tightening action will be at least partially lost.